A survey of the health status of parents and grandparents of cystathionine synthase deficient patients is being continued. The aim is to determine whether heterozygotes for this genetic defect are at increased risk for coronary artery disease. By appropriate physician contact we have now been able to obtain responses from more than 190 families with homocystinuric patients, 113 with new-mutation achondroplastic dwarfism, 125 with hyperphenylalaninemic, and 35 with cystinotic children. Most of the information has been entered in a computer and a preliminary analysis carried out. This preliminary analysis suggests that the questionnaire approach has yielded valid data since the findings in the control groups are reasonable in comparison with data obtained in more elaborate epidemiological studies. It appears, also, that interpretation of the data will be made more rigorous by (a) addition of further control families (b) documentation of the ages at which initial coronary attacks occurred in fathers who have had non-fatal attacks of this kind, and (c) obtaining approximate years of birth and death for grandparents for whom such dates are not known exactly. Efforts to obtain such information are now underway.